Paper pulp and process of making same



Patented Mar. 1, 1932 PATENT ,orrlcr.

LEWISL. ALSTED, OF .APPLETON, WISCONSIN PAPER PULP AND PROCESS OF MAKING SAME No Drawing.

This invention relates to a new article of commerce, namely, dry mechanical or ground wood pulp susceptible of ready, quick and economic re-pulpin for subsequent use 1n 5 the manufacture 0 .paper, board, or other fibrous products and to improved processes for the production and manufacture thereof.

Due to the ease and low cost ofproduction, its light color, excellent printing qualities, et cetera, ground wood or so-called mechanical pulp forms an important constituent in the manufacture of many forms and grades of paper.. It forms about of the pulp stock used in the manufacture of newsprint paper and from to of the pulp stock from which the cheaper rades of socalled wall paper are. made, an it forms the major constituent in the manufacture of various and sundry other types and grades of pa r. Its importance in the industry is, there ore, great and as will be appreciated the cost to the consumer of paper containing ground wood pulp' is largely influenced by and dependent upon the cost'to the paper manufacturer 0 such pulp.

As is well known in theart, very few species of wood can be used in the manufacture of a 'satisfactory ground wood pulp. In years gone by when these species were plentiful in certain sections of this -"country, many paper mills were built in locations accessible not only to this wood supply but also to the paper markets. There was no occasion for longhauls of the raw materials. The pulp was produced at the aper mill from raw material obtained close y and from the pulp the paper .stock was pre ared and paper produced all in a substantia y continuous rocess or operation. These were ideal conditions from the manufacturin standoint and the paper was produce at the owest possible cost. Under this order of things, however, the raw material su ply me removed farther and farther fiom the paper mill, occasioning' added costs due to the radually increasing distances the material had to hauled or transported.

These conditions have perslsted for many years with the result that today the supplies of these species of wood-which are relied Application filed January 28, 1928. Serial No. 250,348.

upon in the manufacture of ound wood pulp are situated at great dlstances from most of the mills in this country. This means that in order to do b siness in face of the competition now offere for instance by the Canadian paper mills located at or near a source of supply and therefore enjoying the ideal manufacturing conditions which formerly obtained in this country, the mills in this country, manufacturers of newsprint paper in particular, are compelled to do business on such a small margin that many of them have been forced to shut down, and it is generally believed that unless relief is shortly forthcoming, it is only a question of time before the others will be forced to do-likewise.

In order to operate under present conditions, the newsprint mills in this country must either have the raw material shipped to them over long distances or else purchase prepared ground wood pulp in the form now commercially obtainable from .pulp mills situated at or near a source of supply. The first is out of the question in the manufacture of newsprint paper and other papers containing a high percentageof ground wood as the freight and other costs incident to the hauling and handling of the raw material would run the costof the paper above present market prices, and the second, also chiefly because of the freight consideration, is not, from a sound business point of view, feasible in competition with paper made at or near the source of supply, because of the fact that ground wood pulp as now 'manufactured must be kept in a wet condition from the time it is made until it is used at the paper mill and for that reason it is necessary to ship approximately from one to twotons of water in the pulp for every ton of pulp. This of course necessitates the payment of freight charges two or three times greater than would be required for the net amount of pulp present in any shipment and constitutes avery heavy burden on the paper manufacturer.

It has long been realized that a great saving in the cost of paper having a high ground wood content could be effected if the pulp could be dried to atmospheric dryness, or substantially so, before shipment, without deterring or preventing subsequent re-pulping at the paper mill. Many have tried to dry ground wood pulp and ship it in that condition and the literature in the industry concial manufacture and sale of dry mechanical pulp and of the various attempts as recorded in the literature pertaining to the industry and of the actual commercial attempts to which I havereferred, I am not aware of a single practical or successful solution of the problem nor am I aware of ground wood pulp ever having been treated or manufactured in such form that it could be thoroughly dried and subsequently, readily, quickly, economically and thoroughly re-pulped and returned to its original pulp condition such as is necessary before it can be used in the manufacture of satisfactory paper at the paper mill.

It has been found and is well known throughout the industry that ground wood pulp dried before use in paper making will not come back or re-pulp to its original con dition on wetting in the beater or otherwise and with the employment of any reasonable amount of treatment the paper made therefrom is marred by small lumps of pulp formed of little dry sections or pockets in the pulp mass which do notand will not break down or separate satisfactorily during the 0 re-pulping operation. Ground wood pulp is made by a purely mechanical grinding oper-- ation in which substantially none of the intor-cellular matter is destroyed or removed. This inter-cellular matter includes resinous 5 binding substances which become interspersed or distributed throughout the ground wood, and in any attempt to dry the resultant pulp, there is a decided tendency for fibers to compact or consolidate and due to the presence of this inter-cellular matter, fibers become glued or bound together in a mass which is more or less impervious to moisture and not susceptible of being broken down or having its fibers satisfactorily separated in a beater 5 or any other apparatus, such as would be used in the re-pulping operation. It is for these reasons that it has heretofore been necessary to ship the ground wood in a wet condition in the form of blankets vor laps go containing approximately from to 60, andeven 75, percent of moisture.

One object of my invention is to provide as an article of commerce dry ground wood pulp which may be manufactured at a raw material mill located at a source of the necessary species of wood and shipped any distance to a paper mill and which will have the property of being capable of ready, economical and complete re-pulping in the manufacture of paper.

Another object of my invention is to provide improved processes for the treatment and manufacture of ground wood pulp so that it maybe completely dried, or dried to atmospheric dryness, and left inthat condition indefinitely or for any length of time required and which may be readily, quickly and economically re-pulped and returned to its original pulp condition.

A further object of the invention is to provide as a new article of commerce a dry pulp mixture containing predetermined percentages of ground wood and sulphite or other chemical pulp, the mixture being susceptible of thorough and complete re-pulping at the paper mill and the immediate manufacture therefrom of paper, newsprint for instance, without the addition of any other pulp or other ingredients to the mixture.

In view of the conditions existing in the industry, as previously described, the advantages of the above will be apparent and it is ventured that the resultant savings to the paper mills of this country, particularly manufacturers of paper having a high ground wood content such as newsprint paper, will enable such mills either to continue or reopen operations in face of the competition referred to and on a basis which will net them a fair return on the amount of capital invested.

I shall now proceed to a disclosure of several processes as illustrative embodiments of my invention.

I have discovered that by adding a small amount, say 20% of sulphite or other chemical pulp or cellulose fibers to ground wood, the resultant pulp may be dried to substantially atmospheric dryness and yet be capable of easy, quick and economic re-pulping without the appearance of specks or lumps, either in the re-pulped mass or in the resultant paper, such as invariably occur in the pulp and, paper resulting from untreated ground woodwhich has been dried. In carrying out this process, I provide a suitable mixing tank into'which the given quantities of the ground wood and chemical or other cellulose pulp, each preferably in slush form, may be con- 'veyed. Suitable agitating means may be used to advantage in the mixing tank for stirring the two pulps so as to produce a thorough and uniform mixture. I then convey the mixture to alap or web forming apparatus (wet machine) of any of the well known types, such apparatus usually including a tank into whichthe slush pulp is.flowed, and

aperforated suction cylinder or drum which revolves in the tank partly submerged in the pulp so as,.to cause the latter to be deposited free of a large percentage of its water on the pulp in any well known manner may be stripped from this cylinder in a continuous web or. sheet and conveyed on the usual endless belt or apron between press rolls and delivered either in sheets or so-called noodlelikefragments such as would result in well known manner from the use of a doctor or similar device in conjunction with one of the press rolls. As the pulp, free of. a large percentage of the water issues from the press rolls of the wet machine, it may be conveyed either to a shredding machine where the sheets or fragments are shredded and then through a suitable drying tunnel or other drying apparatus or direct to a drying apparatus. It is preferred to dry the pulp to atmospheric dryness, or substantially so, after which it is ready for shipment or for storage. The resultant dry pulp product may be either in the form of shredded fragments or pieces such as would result from the use of a shredder previous to' the drying step, or it may be in the form of the larger noodle-like fragments, such as would result from passing the pieces of pulp which would result from doctoring the pulp from one ofthe press rolls direct to the drying apparatus, or it may be in the form of a rolled sheet if the pulp is taken from the wet machine in a continuous web or sheet and passed as such. through the drying apparatus,

. 1 to 4 square feet or larger, such as would result by cutting the-web or sheet before or after it leaves the wet machine into sections of the desired shape and size and then passing such sections through the drying apparatus, or such as would result from passing the continuous web or sheet through the drying apparatus and then severing or cutting the driedsheet into sections'of the desired shape and size.

It will be appreciated from-the above that the process described is characterized chiefly by the mixing of a given amount, say of ground wood pulp-in slush form with, a given amount, say 20%, of chemical pulp such as sulphite or other cellulose fiber pulp in slush form and subsequently removing the water therefrom and drying the pulp to substantially atmospheric dryness for shipment or storage. It will also be appreciated that in carrying out the process I am in no way limited or restrictedto any particular type or types of appartus which may be employed. The art abounds in various forms of apparatus suitable for carrying out each step of the process and a choice of any of these is of course within the contemplation of the invention. .Neitheris it desired to limiter restrict the process in any way to the particular percentages mentioned of ground wood and chemical pulp. Twenty percent of the chemical or other cellulose fiber pulp has been found in actual tests to give very satisfactory results. Other percentages, however, will also give satisfactory results, and from a commerclal standpoint, it may be desirable to keep the percentage of chemical pulp down as low as may be consistent with good results so that the resultant product will be universally usable throughout the paper makin industryin the manufacture of all groun wood content papers. 1

So far as I am aware, ground wood is seldom, if ever, used alone in the manufacture of paper or paper products. A paper might be made of all ground wood content, but it would be so inferior and lacking in strength that it would be of no practical utility. From 15 to 50% of sulphite or other chemical pulp or cellulose fiber is usually mixed with the ground wood by the paper manufacturer to .give strength to the paper. Standard newsprint paper embodies about 20% sulphite pulp and 80% ground wood. Therefore, for the newsprint paper mills ground wood pulp to which had been added 20% of sulphite pulp would be the ideal mixture, because the dried product could then be re-pulped at the paper mill and made directly into paper without the addition of any other materials. Board and some of the cheaper grades of wall paper, however, contain as low as 15% and possibly less of sulphite or other chemical pulp or cellulose fiber and it may be desirable in commercial use'of the invention to n'tianufacturea separate grade of dry ground wood pulp containing less than20% chemical pulp, say 15% or even 10%, for paper mills manufacturing paper or board with an or ground wood content.

However, tests and experiments which have conducted indicate that the addition of only 15% or less of the chemical pulp to the ground wood does not give as satisfactory a product as the 20% mixture, but I have further discovered that by adding a small percentage,'4 to 6%, for instance, of colloidal clay, such as bentonite, to mixtures of ground wood and chemical pulp in which the percentage of the latter is so small asto render the mixture otherwise inferior to the more desirable 80% ground wood20% sulphite mixture, the conditions are greatly improved, resulting in a product fully as good, if not better, than the mixture comprising merely 80% ground wood and 20% sulphite. The latter mixture, however, has been found to be entirely satisfactory for re-pulping after dry- 20 to 50%, or. greater, could be used in the mixture with entirely satisfactory results.

In other words, the

In mixtures where the chemical pulp constitutes appreciably less than 20%, I add, as above pointed out, a small percentage of a colloidal substance, such as bentonite, which I have found renders such mixtures capable of easy and quick re-pulping after they have been dried.

I have further discovered that by mixing with ground Wood pulp a small percentage of colloidal clay, such as bentonite, Without the'addition of chemical pulp or any other material, the ground wood pulp may be thoroughly dried for shipment or storage and that it may subsequently be easily re-pulped preparatory to the manufacture of paper. In this connection I have found that from 6 to 8% of bentonite gives very satisfactory results, although I do not desire to be limited to these exact percentages. The bentonite or clay seems to have the effect of preserving an even distribution of the pitch, albumen and other inter-cellular and water resistant substances in the groundwood, so that after it has been dried andsubsequently immersed in water, it will Wet and absorb evenly without forming the dry water resistant sections or pockets previously described in connection with ordinary ground wood.

When using bentonite in my processes, I prefer to prepare it as follows A portion of this material in its natural state, usually in a hard dry semi-rock like form is broken up and then ground or otherwise reduced to a finely divided condition. It is then mixed with water and in this form added in the proper percentage to the pulp while the latter is still in slush form. If desired the bentonite may be ground or otherwise finely divided directly in water or it may be added in a dry finely divided form directly to the pulp slush.

According to my processes, as above set forth, it will be appreciated that I am enabled to produce as an article of commerce dried paper pulp comprising either ground Wood alone or ground wood with varying percentages of sulphite or other chemical pulp or cellulose fiber and that in the case of the ground wood and chemical pulp mixtures the "percentages may be accurately determined and controlled.

Theaddition of sulphite or other cellulose fiber and/or a colloidal substance'such as bentonite, in small quantity to the ground wood prior to drying will in no way have any injurious effect upon the resultant pulp or paper. On the other hand, it' is in fact an advantage in that it may be the means of shipping to a paper mill a dry pulp mixture which may be directly made into paper or board of its specifications without-the addition of any other pulp, fiber, or other materials. Furthermore, the 'mixture according to the present invention being eifected with the pulps in slush form, it is entirely feasible to control the exact percentages desired with predetermined accuracy, which is also a substantial advantage in the dry pulp.

Just why the addition of a small amount of chemical pulp or other cellulose fiber to the ground wood with or without a small amount of colloidal clay, or the addition of a small percentage of colloidal clay alone prevents the ground wood from compacting, consolidating and adhering or the fibers thereof becoming glued together in a wood-like mass approximating its original natural condition is not known, but actual tests and experiments have shown conclusively that such action is thereby overcome and the ground wood preserved in such condition that it may be quickly, economically and thoroughly re-pulped and worked up in standard beating equipment at the paper mill and satisfactory paper or board products produced therefrom. The chemical or cellulose fibers seem to act as canals to conduct Water into every portion of the dried pulp and it consequently absorbs water quickly and evenly without the formation of sections or pockets of dry pulp as is the case with sheets, flakes or fragments made up entirely of ground wood, while a colloidal substances such as bentonite seems to have the property of effecting and preserving an even distribution of the pitch, albumen and other inter-cellular and water resistant substances in the ground wood so that after the pulp has been dried it will, when immersed in water, wet, absorb and break down quickly and easily into its original pulp condition.

Pulp manufactured according to any of the above processes may be produced in any desired form including the various forms above named-shredded, creped, continuous rolled sheets, regular shaped sections of appreciable area, or fragments such as would result from the use of a doctor or scraper in conjunction with one of the press rolls of the wet machine. The pulp in sl1redded,'creped, or similar form. may be conveniently baled or bundled for shipment while-the pulp, if in uniform sections of appreciable area, may be suitably stacked and wired or otherwise tied into bundles of desired size or weight.

It is not desired nor intended that the several processes I have described above shall in any manner limit or restrict my invention,

that the same be construed to include any colloidal clay or substance such as silica gel, aluminum hydroxid, and et cetera. In its broadest aspects my invention contemplates 1 all of these various materials and/or their equivalents used either alone or in combination in the manufacture of dry pulp, the basic feature of the invention residing in the mixing with ground wood pulp any substance having the property of rendering said pulp, when dry, uniformly pervious to water and readily returnable to its original pulp condition. The invention also contemplates, as a new article of commerce, the resultant pulp product having the characteristics and properties above pointed out regardless of how the same may be produced or manufactured.

The invention claimed is:

1 A process for they manufacture of dry mechanical pulp, consisting in first prepar: ing ground wood in slush form, then mixing therewith a substance capable of entering into a final product made from the pulp having the property of rendering said pulp, when dry, uniformly pervious to water and readily returnable to its ori inal pulp condition, and then-drying the pu p to substantially atmospheric dryness.

2. A process for the manufacture of dry pulp for subsequent re-pulping in the manufacture of paper, board and other fibrous products, consisting in first preparing ground wood in slush form, then preparing chemical pulp in slush form, mixing the two together in definite proportions while in such form, and then drying to substantially atmospheric dryness.

3. As a new article of commerce, a dry pulp mixture containing substantially 80% ground wood and substantially 20% chemical pul 4. As a new article of commerce, a dry pu p mixture containing ground wood and substantially resin-free pulp.

. 5. As a new article of commerce, a dry mechanical pulp containing ground wood and a colloidal clay.

6. As a new article of commerce, a dry pulp mixture containing ground wood and sulphite.

7. As a new article of commerce, a dry inechanical pulp containing ground wood and a small percentage of bentonite.

8. As a new article of commerce, 9. dry pulp mixture containing ground wood, a chemical pulp and a colloidal clay. ,1?

9. As a new article of commerce, a dry pulp mixture containing substantially 80% ground ,wood and substantially'20% sulphite.

10. As a new article of commerce, dry ground wood pulp containing a substance 'capable of entering into a final product made from the pulp having the property of rendering said pulp, when dry, uniformly pervious to water and readily returnable to its original pulp condition.

11. A process for the manufacture of dry pulp for subsequent .re-pulping in the manufacture of paper, board and other fibrous products, consisting in pre aring ground wood in slush form, then a ding thereto a small percentage of bentonite in finel divided form and evenly distributing the same throughout the pulp, and then drying the pulp to substantially atmospheric dryness.

12. A process for the manufacture of dry' pulp for subsequent re-pulping in the manufacture of paper, board and other fibrous products, consisting in first preparing ground wood in slush form, then pre aring a chemical pulp in slush form, mixmg the two together in definite proportions while in suchform and adding a small rcentage of a colloidal clay in finely divi ed form, and then drying the pulp tosubstantially atmospheric 14. As a new article of commerce, a dry pulp susceptible of nick and economic repulping in the manu acture of paper, board and other fibrous products, comprising ground wood and a colloidalsubstance hav ing a property of effecting and preserving an even distribution of the pitch, albumen and otherinter-cellular substances in the round wood so that the pulp when subjecte to the re-pulping operation will wet, absorb and break down quickly and easily into its original pulp condition.

1-5. As a. new article of commerce, a dry pulp susceptible of I nick and economic repulping in the manu acture of paper, board and other fibrous products, comprising.

ground wood, highly absorbent cellulose fibers, and a colloidal substance in finely dividedform, the latter having the property of effecting and preserving an even distribution of the pitch, albumen and other intercellular matter present in the ground wood and the fibrous material liaving the property of quickly and evenly conducting water throughout the pulp when the latter is subjected to the re-pulping operation.

16. A process for the manufacture of pulp .whichmay be completely dried and subsequently re-pulped in the manufacture of paper, board and other fibrous products, which process consists first in preparing ground wood in slush form, then preparing chemical pulp in slush form, then mixing the two in approximately the proportion of four parts ground wood to one part substantially resin-free chemical pulp, then partly removing the water from said mixture, and

then drying to substantially atmospheric dryness.

17. As a new article of commerce, an air dry pulp mixture containing ground wood and cellulose fiber, the cellulose fiber bein thoroughly interspersed with the groun Wood fiber to prevent interadhesion between the wood fibers.

In witness whereof, I hereto aifix my signature.

LEWIS L. AL STED. 

